The present invention relates to an ion implanting unit utilizing a radio frequency linear ion accelerator, and relates more particularly to an ion implanting unit suitable for generating a high energy ion beam having a large current.
An ion implanting unit utilizing a conventional radio frequency quadrupole (RFQ) ion accelerator is disclosed in Japanese Patent Unexamined Publication No. JP-A-60-121656. This prior art technology has a characteristic that it can implant high-energy ions having an energy in the range of several hundred keV to several MeV.
FIG. 3 is a block diagram for showing the configuration of the prior art technology.
As shown in this drawing, the conventional ion implanting unit has a basic structure which includes an ion source 1 for generating ions to be implanted into a material to be processed in a vacuum, a sector-type mass spectrometer 6 for carrying out mass spectrometry of an ion beam that has been extracted from this ion source 1, an RFQ accelerator 3 for accelerating ions produced from this mass spectrometer 6 with a radio frequency voltage, and an ion implanting chamber 4 for implanting ions outputted from this RFQ accelerator 3 into the material to be processed.
A conventional example of the case where a quadrupole lens is disposed between the mass spectrometer 6 and the RFQ accelerator 3 for the purpose of converging an ion beam that has been injected into the RFQ accelerator 3 is disclosed, for example, in Nuclear Instruments and Methods in Physics Research B50, 1990, pp. 478-480.
As described above, all of the prior art techniques employ a sector-type mass spectrometer 6 in order to select desired ions out of various kinds of ions which are included in the ion beam that has been extracted from the ion source 1.
Also, when the quadrupole lens is disposed between the mass spectrometer 6 and the RFQ accelerator 3 for the purpose of converging the ion beam that has been incident to the RFQ accelerator 3, all of the prior art techniques employ an electrostatic quadrupole lens as shown in Nuclear Instruments and Methods in Physics Research B37/38, 1989, pp. 94-97.
As described above, according to the prior art techniques, the use of the RFQ accelerator makes it possible to implant high-energy ions but the ion beam that has been extracted from the ion source 1 is not utilized to the maximum extent, so that a current value is reduced to half or below during the passage of the beam from the ion source 1 to the ion implanting chamber 4, with a result that a large current cannot be obtained. The above problem occurs for the following reasons. In the example of FIG. 3, the sector-type mass spectrometer 6 is used to carry out mass spectrometry of the ion beam that has been extracted from the ion source 1. The sector-type mass spectrometer 6, however, provides low transmissivity because it utilizes a weak convergent lens. Further, when the electrostatic quadrupole lens is disposed between the mass spectrometer 6 and the RFQ accelerator 3, the electrostatic quadrupole lens separates electrons in the beam, and therefore it is not possible to restrict the divergence of the beam due to the space charge effect, with a result that the ion beam cannot be sufficiently converged to the incident opening of the RFQ accelerator 3.